Thermostats



y 27', 1965 B. R. LEIGH ETAL 3,

THERMOSTATS Filed April 27, 1-962 FIG 2 FIG-.I

United States Patent 3,196,685 THERMDSTATS Bertram Robert Leigh, 12 Beacon Way, Rickmansworth, England, and Leonard George Thomas, 71 Edward St, Depttord, London SE. 8, England Filed Apr. 27, 1962, Ser. No. 190,744 Claims priority, application Great Britain, May 1, 1961, 15,717/ 61 2 Claims. (Cl. 73-3614) This invention concerns improvements relating to thermostat and like temperature-sensing devices, particularly mercury-in-glass thermostats. For adjusting or changing the setting of such a thermostat, it has been common heretofore to provide a small resistance heater wound round an auxiliary temperature-sensitive bulb of the thermostat.

In accordance with the present invention, the Peltier therm-o-electric, heating or cooling, effect produced at a semi-conductor junction or junctions by a low-voltage direct current is employed for adjusting or changing the setting of the thermostat or like temperature-sensing device.

While the invention is applicable in especially convenient manner to thermostats of the mercury-in-glass type, it can also be employed with other types of thermostat, for example of the bimetal type, the type operated by gas or liquid pressure, the liquid and gas type, the thermoelectric or thermo-couple type and the resistance type, the last including such thermostats as operate in conjunction with resistances of the kind known by the registered trademark Thermistor and made by Standard Telephones and Cables Ltd., especially thermostats employed for low and medium temperatures. Furthermore, the invention can be applied to the control of the setting of thermostats or temperature-sensing devices employed in known manner as time-delay units.

For the purposes of the invention, Peltier elements can be used singly or with two or more elements cascaded, that is with the cold end of one element connected to the hot end of the next in per se known manner.

One manner of carrying the invention into effect, as applied to a mercury-in-glass thermostat, will now be more fully described by way of example and with reference to the accompanying drawing, in which:

FIGURE 1 is a side elevation,

FIGURE 2 a front elevation, and

FIGURE 3 a plan view of the thermostat.

In this example, the auxiliary or bias bulb 1 of a thermostat 2 having a main bulb 3 exposed to a controlling temperature condition is embraced by a beryllium-copper heat conductor 4 which serves to conduct heat between the bulb 1 and a semi-conductor device comprising two thermo-electric elements 5, 6. This conductor 4 also serves as the electrical junction between the elements 5, 6. As illustrated, the conductor 4 takes the form of a strip substantially completely surrounding the bulb 1 (FIG- URE 3) and having out-turned feet 7 by which it is attached directly to the adjacent ends of the elements 5, 6. These take the form of blocks, extending parallel to each other and approximately radially of the bulb, of P-type and N-type semi-conductor material respectively, designed to give a high, or the maximum, Peltier effect. The other ends of the blocks 5, 6 are attached directly to heat sinks, conveniently in the form of copper plates 8, for conducting or transferring heat between respective blocks 5, 6 and the atmosphere. Electrical connections to the semi-conductor device are made by leads 9 attached to the plates 8. The region surrounding the auxiliary bulb 1, the heat conductor 4 and adjacent ends of the semi-conductor blocks 5, 6 is thermally insulated against the surrounding region by being embedded in or enclosed by insulation, as

indicated diagrammatically at 10. The whole thermoelectric arrangement can bemade quite small. The contacts of the thermostat 2 are indicated at 11.

The leads 9 will be connected in a circuit by which a low-voltage direct current supplied to the elements 5, 6 can be set or varied by either manual control means or automatic control means influenced by a variable factor, the nature of this factor being determined by the particular function which the thermostat is required to serve. The circuit in which the thermostat contacts 11 are connected will likewise depend upon the function to be served.

Biasing of a thermostat by the Peltier eifect involves some departures from current biasing technique and also offers various important possibilities not available with the latter. The following points may be mentioned:

A thermostat can be biased in either direction, i.e. its auxiliary bulb can be cooled and/or heated, depending upon the direction of the current through the thermoelectric elements. Cooling raises the setting or control point of the thermostat from the normal value and heating lowers it.

The bias current will generally be higher than that at present used, say up to about 1 amp. The bias-voltage drop will be lower than the typical 12 volts drop used on a 660 ohm thermostat for about 16 F. set-down.

Provided that the set-down or set-up is kept fairly small, it will be roughly proportional to the first power of the biasing current, instead of being proportional to the square of the current, to about F. set-down, as at present. The approximately linear relationship can greatly simplify the calculation and application of bridge or other circuits used in temperature-control equipment.

The slope of the set-doWn/current relationship in the bias heating direction becomes with larger bias set-downs or set-ups, somewhat steeper than the slope of the set-up/ current relationship in the bias cooling direction owing to the difference between the heating and cooling co-eflicients of performance with reversible heating and cooling equipment. However, provided the bias is kept small, the difference in slope is not disturbing.

It is possible, by providing for biasing upwards and downwards, so to operate a thermostat that it is always fairly close to its natural setting. Error in temperature setting similar to that arising at present due to error of the K (bias sensitivity) factor can be reduced by this means.

It is also possible to achieve symmetrical stabilisation, i.e. stabilisation in the less-heat direction as well as in the more-heat direction of a heating or cooling equipment, on a positioning type of controller, such as is frequently used for temperature control on aircraft, and in pressureventilation systems for railway-carriage heating and ventilation, without needing a regulated-voltage supply for feeding the bias arrangements.

On a more-heat signal, heating bias will be applied and on a less-heat signal cooling bias. The bias for the intermediate dead-band determines the operational zone of the thermostat and the thermostat will work between its natural settings if there is no dead-band bias.

Provision can easily be made for linear reheat compensation circuits, such as may be required with individnail-compartment temperature control in a railway vehicle, for example. When Peltier bias in the cooling direction is used for this purpose on a main thermostat, or thermostats, the signal represented by, or derived from, the total reheat current for all the compartments does not have to be inverted before being used for biasing the thermostat. An amount of elevation of the setting of the main thermostat proportional to the average elevation of the temperature of the individual compartments is secured directly.

We claim:

1. A thermostat device provided with means for ad- .13 A, justing its temperature setting, comprising a temperature References Eited by the Examiner sensing element, two semi-conductor elements, of P-type UNITED STATES PATENTS and N-type respectively, thermally connected with a conductor which embraces the said temperature-sensing ele- 2158146 5/39 Parks et 73*368 2,871,376 1/59 Kretzmer 73-362 men n meq sf r s pplymg a l w-v ge lr c r- 5 3,017,522 1/62 Lubgks 317*235 rent to the said unctions, whereby the Peltier thermov electric effect produced at the said junctions is effective OTHER REFERENCES for adjustingthe said temperature setting. 629,628 10/61 Canada.

2. A device as claimed in claim 1, wherein the said a conductor and the said semi-conductor and temperature- 10 IQAAC LISANN Prlmary Examine"- sensing elements are surrounded by thermal insulation. ROBERT B, HULL, Examiner, 

1. A THERMOSTAT DEVICE PROVIDED WITH MEANS FOR ADJUSTING ITS TEMPERATURE SETTING, COMPRISING A TEMPERATURE SENSING ELEMENT, TWO SEMI-CONDUCTOR ELEMENTS, OF P-TYPE AND N-TYPE RESPECTIVELY, THERMALLY CONNECTED WITH A CONDUCTOR WHICH EMBRACES THE SAID TEMPERATURE-SENSING ELEMENT, AND MEANS FOR SUPPLYING A LOW-VOLTAGE DIRECT CURRENT TO THE SAID JUNCTIONS, WHEREBY THE PELTIER THERMOELECTRIC EFFECT PRODUCED AT THE SAID JUNCTIONS IS EFFECTIVE FOR ADJUSTING THE SAID TEMPERATURE SETTING. 